Put the apples in a large bowl. Add ½ cup brown sugar, ½ cup flour, lemon juice, ½ teaspoon apple pie spice, ½ teaspoon cinnamon, and ¼ teaspoon salt. Mix well. Pour the apple mixture into a 9- x 12-inch baking dish that has been sprayed with cooking spray.
In a medium bowl, whisk together the remaining ¾ cup of brown sugar, 1 cup of flour, ½ teaspoon apple pie spice, ½ teaspoon cinnamon, ¼ teaspoon salt, and the baking powder. Add the melted butter, and whisk the mixture until it is well combined and crumbly.
Spread this crumb mixture on top of the apples in the baking dish. Bake for 45 minutes, until the top is golden brown.